Lasagna with Slow-Roasted Tomato Sauce

Slow-roasting the tomatoes gives the tomato sauce for this lasagna recipe an intense depth of flavor—which is then enhanced by the umami in onions, Parmesan and spinach. The lasagna noodles are layered into the lasagna uncooked; the moisture from the fresh spinach cooks them perfectly as the lasagna bakes in the oven.